Break out of speculative parsing on bad parameter initializer (#19158)

* Break out of speculative parsing on bad parameter initializer

* Remove uses of 'finally'

* give up -> stop

* Do without exceptions

* Remove `resetAfterSpeculation`

* Use Fail and FailList objects

* Remove `inSpeculation` parameter to parseDelimitedList

* Don't use `createNodeArray`, it's not always in scope

* Move Fail and FailList inside initializeState

* More code review

* More code review

Author: Andy